Control system for a hydraulic motor

ABSTRACT

The present invention relates to a hydraulic system and, more particularly, to a system for reciprocating a machine tool table or the like, including a cylinder, a main control valve, and a pilot valve, all operatively connected together.

United States Patent [151 3,685,395 Straub et al. [4 1 Aug. 22, 1972 1 CONTROL SYSTEM FOR A [56] References Cited HYDRAULIC MOTOR UNITED STATES PATENTS [72] Inventors: Bruno E. Straub; William II. 659 712 10/1900 9 H 14 G t Id, b th f t '1 es 1 1?" 0 0 1,493,418 5/1924 Arrowsmith ..91/314 1,617,516 2/1927 Farquhar ..91/314 [73] Assign e: Cincinnati Mila mn-H ald Corn, 2,933,105 4/1960 Jermann ..91/216 B Worcester, Mass. Filsd Dec 14 1970 FOREIGN PATENTS OR APPLICATIONS A N 97 5 179,570 5/1922 Great Britain ..91/286 Primary Examiner-Paul E. Maslousky Related US. Application Data Atmmey NOrman S. Blodgett [63] Continuation-in-part of Ser. No. 791,352, Jan.

15, 1969, abandoned. [57] ABSTRACT I The present invention relates to a hydraulic system [52] US. Cl. ..91/216 B, 91/219, 991l//22886gs and, more particularly, to a System for reciprocating a machine tool table or the like, including a cylinder, a 11 F'ilifi'fss'ra;11:5151??255215312 i??? main valve and a Pilot valve operatively connected together.

8 Claims, 10 Drawing Figures PATENTEDwcza m2 SHEET '1 OF 4 INVENTORS Brmvo EiSrRAue WILLIAM H. GROTEWOLD ATTORNEY PATENTEDwszz I972 SHEET 2 [1F 4 FIG.6.

CONTROL SYSTEM FOR A HYDRAULIC MOTOR CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION In the operation of a machine tool such as a grinding machine, it is important that means be provided to subject a table, such as a wheelhead table, to reciprocation. In the case of a grinding machine, this reciprocation would be used to pass the abrasive wheel back and forth over the surface to be ground. It has been common practice to actuate the table by use of a hydraulic cylinder which is operated by a main valve controlled by a pilot valve. Such prior art devices have suffered from a number of deficiencies; for instance, the reversal of the cylinder produces a shock in the system which can have deleterious efiects on the quality of the ground surface being produced. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a hydraulic system for use in the reciprocation of a machine tool table, where the valve decreases the velocity of the table gradually to zero and, then, without delay, gradually speeds up the table in the opposite direction; during this cycle, the table does not receive severe shocks due to sudden changes in the oil pressure in the table cylinder.

Another object of this invention is the provision of a hydraulic table drive, wherein severe shocks during table reversals are prevented throughout an entire range of table speeds to insure a smooth machine operation.

A further object of the present invention is the provision of a hydraulic system for a machine tool table drive, wherein the table positions at the reverse points are repeated accurately for each stroke and table speed; this table position varies very little as the table speed is changed during the machine tool machining cycle.

It is another object of the instant invention to provide a hydraulic system whose principles of operation can be used with various hydraulic operating pressures and different types of table way bearing systems.

A still further object of the invention is the provision of a hydraulic system for the reciprocation of a machine tool table, which system includes a tarry con trol which makes it possible to cause the table to dwell for a selected time independently at each end of the table stroke.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

SUMMARY OF THE INVENTION In general, the invention has to do with a hydraulic system for reciprocating the table of a machine tool, including a table cylinder and a main control valve having a housing in which a spool reciprocates, there being end chambers formed in the housing into which the ends of the spool extend. A pilot valve is provided having a housing in which a spool reciprocates and a mechanical linkage joins the two spools, the table operating the linkage during certain portions of the cycle of table reciprocation and the spool of the pilot valve operating the linkage during other portions of the.

cycle. A hydraulic connection between the end chambers of the main control valve includes a means for controlling the flow of fluid from one chamber and the flow of fluid into the other.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings, in which:

FIG. 1 is a somewhat schematic view of a hydraulic system embodying the principles of the present invention,

FIG. 2 is a horizontal sectional view taken on the line II-II of FIG. 1,

FIG. 3 is a horizontal sectional view taken on the line III-III of FIG. 1,

FIG. 4 is a schematic chart showing table movement,

FIG. 5 is a schematic view of a modified form of the invention,

FIG. 6 is a schematic view of another modification of the invention.

FIG. 7 is a schematic view of a further modification of the invention,

FIG. 8 is a schematic view of a further modification of the invention,

FIG. 9 is a schematic view of a still further modification of the invention, and

FIG. 10 is a schematic view of another modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, which best shows the general features of the invention, the hydraulic system is shown in use with a machine tool table 1 having downwardly-dependent dogs 2 and 2. Dog 2 is capable of swinging upwardly into the table. A valve lever 3 is mounted on a rotatable shaft 4 with its upper end in position to be engaged by either the dog 2 or the dog 2'. Also mounted on the shaft 4 for rotation therewith is a link 5 and an actuating handle 4'. The upper end of the link is pivotally connected to the spool 6 of a main control valve A, while the lower end is similarly connected to the spool 7 of a pilot valve B.

Exhaust ports 8 and 12 of the main control valve are connected by a line 25 through a speed control and cutoff valve 25a to sump. A pressure inlet port 9 is connected by a line 10 to a source of pressure fluid including a pump 10a. The main control valve A is connected by flexible hoses in the usual way to the opposite sides of the piston of the table cylinder 11 to connect them alternately to the pressure inlet port 9 or the exhaust ports 8 and 12.

A pressure line 14 is connected to the source of pressure fluid and to a pressure inlet port 22 which is operative on a portion of the pilot valve B to move the spool 7 one way or the other. Surrounding the ends of the spool 7 are chambers 15 and 16 which are connected by lines and valves, such as a line 23 and a throttle valve 21, to their respective sides of the piston portion of the valve; in each instance, a check valve by-passes the throttle valve. A line joins the line 23 back to a port 24 in the valve and a similar line and port is located on the other side of the valve adjacent the chamber 15.

The opposite ends of the spool 6 of the main control valve reside in chambers 19 and 20, and these chambers are joined by a means, such as the line 18 with a throttle valve 17, for controlling the flow of fluid out of the chamber 19 and into the chamber 20, or vice verse.

- In FIG. 2 it can be seen that the upper end of the link is provided with a pin 26 which lies in a groove 27 formed on the end of the spool 6. The diameter of the pin is somewhat less than the width of the groove by an amount indicated by the dimension d. For the purpose of illustration, this gap is shown as being quite large, but, in practice, it is in the order of magnitude of .004 inch.

FIG. 3 shows that the pivotal connection between the lower end of the link 5 and the spool 7 of the pilot valve B consists of a cylindrical pin 28 engaging a groove 29 formed on the spool. The pin is provided with an eccentric shank 31 carried snugly in a bore in the link and locked in a predetermined angular position of adjustment by a set screw. The width'of the groove 29 is exactly the same as the diameter of the pin 28, so that angular adjustment of the pin 28 brings about an adjustment of the relationship of the spool to the link for the purpose of correcting misalignment.

The operation of the system will now be readily understood in view of the above description. Although the valve 25a is shown as manually operated, it can be assumed that the grinding machine with which the system is used has the usual control circuits in addition to those shown in the present application and that one of these circuits may by remote control cause the opening or closing of the valve. The valve 25a lies between the drain ports 8 and 12 of the main valve A and the fluid storage sump and is used not only as a shut-off valve, but also as a variable restriction for the speed control.

Let us assume that the table 1, at the time that the valve 25a is opened, lies almost at its central position, this being the position at which it was left when the valve 25a was last closed to stop table reciprocation. The lever 3 is at its right-hand position, i.e., opposite that shown in FIG. 1. The opening of the valve 25a causes the table to travel with a certain speed from the right to the left under the impetus of the table cylinder 11. Under these conditions, the cylinder receives pressure fluid at the left side of the piston. The opening of the valve 25a allows oil to be squeezed out of the right side of the cylinder, through the main control valve A, through the line 25, and through the valve 25a into the sump. The dog 2 on the table eventually engages the upper end of the lever 3 and rotates it (along with the link 5) counter-clockwise about the axis of the shaft 4.

This pulls the spool 6 of the main valve A to the left and pushes the spool 7 of the pilot valve B to the right. This movement of the lever 3 and the link 5 places the system in the condition shown in FIG. 1. The spool 6 of the main valve A has just been moved to its left-hand position, thus reversing the pressure and drain connections to the cylinder 11 to start movement of the table in the other direction, i.e., from left to right. The movement of the lever 3 from right to left is somewhat restricted by the fact that the speed of movement of the spool 6 is limited by the pumping of fluid from the chamber 19 to the chamber 20 through the line 18 and the throttle valve 17. The restriction of the lever is also felt by the table 11; this, combined with the neutral position of the main valve, means that the speed of the table is reduced at the ends of the stroke, so that the possibility of shock is reduced.

Now, while the lever 3 is being moved from right to left at the end of the stroke, the spool 7 is pushed to the right. At the start of this movement to the right, the central land of the spool moves to the right relative to the port 22 and allows pressure fluid to act on the lefthand end of the spool; the fluid passes from the port 22 to the chamber 16 by way of the conduit 23 and the throttle valve 21. At the same time, fluid is being squeezed out of the chamber 15 at the right-hand end, but is allowed to by-pass the throttle valve at that end because of the check valve. In other words, the speed of the spool 7 is detemiined by the setting of the throttle valve 21 during the first part of the end of the table stroke, i.e., the part just after reversal of table motion, which is the part of the cycle just before the lever 3 reaches its extreme left-hand position.

FIG. 1 shows the condition of the system when the lever is slightly more than half way from right to left. In a short while, the land at the left end of the spool will uncover the port 24 and allow pressure fluid to flow without inhibition, thus bringing about a higher speed movement of the spool 7. At that time, the only reduction to movement of both spools is the restriction supplied by the throttle valve 17.

The spool 7 starts its movement to the right at the instant that the table dog 2 strikes the lever 3 and starts to push the lever to the left. Because of the gap d between the surface of the groove 27 in the spool 6 and the pin 26, the movement of the lever 3 and the link 5 does not immediately start the spool 6 of the main valve A on its motion to the left. A short time is required for the pin 26 to engage the left-hand radial surface of the groove 27 to reach the condition shown in FIG. 2. During this interval, the spool 7 has been positively started on its motion to the right at slow speed by fluid arriving at the port 16 by way of the throttle valve 21. This means that the movement of the table 1, the lever 3, and the spool 6 is absolutely controlled by the setting of the throttle valve 21. It also means that the reversal of pressure fluid from one side to the other of the piston in the cylinder 11 takes place at a slow, controlled rate, thus avoiding shock. Once the reversal has been completed at slow speed, the spool 7 reaches the point at which the left-hand land uncovers the port 24 and permits a high speed movement of the spool 7 to the right and of the spool 6 to the left. Shifting the movement of the spool 6 to high speed allows the ports to open more rapidly and the table to accelerate. By the time the lever 3 has reached its extreme left-hand position, the table has started to accelerate in movement to the right and the dog 2 leaves the lever behind.

The normal stroke of the cylinder and movement of the table take place between the time the dog 2 leaves the lever 3 and it is engaged by the dog 2'. When the dog 2' strikes the lever 3 at the end of left-to-right movement of the table 1, the reversal takes place in the same manner as described above, except that the elements involved are reversed. For instance, in the case of the pilot valve B, the slow speed motion is determined by the throttle valve at the right-hand end and the controlled fluid appears at the port 15.

The operation of the system can also be described by reference to the chart in FIG. 4 which shows a typical cycle of table movement. The important points in the cycle are described below:

POINT X Table is stopped at extended run-out, for instance, to change workpieces in a grinding machine. To start the cycle, the operator opens the valve 25a and actuates the handle 4' to move the lever 3 to its right-hand position,so that the main valve A is set for movement of the table to the left. As soon as the valve 25a is opened, the table starts to move to the left. The dog 2" strikes the lever 3, but pivots upwardly out of the way.

POINT Y The dog 2 strikes the lever 3 and starts it to move to the left. POINT 2 Pin 26 strikes the left-hand radial surface of the groove 27 and starts spool 6 moving to the left. POINT R Land 7a of spool 7 uncovers the port 24. POINT Y Dog 2' strikes lever in its left position. POINT Z Pin 26 strikes right radial surface of groove 27. POINT R The land 6a of the spool 6 moves to the right to connect the pressure port 9 to the left side of the cylinder 11 to start movement of the table to the left.

The reciprocation of the table 1 continues in this way as long as is necessary, and then the table moves on an extended traverse to the point X; in order to do this, it is necessary to swing the dog 2 upwardly out of the way of the lever 3.

It should be noted that the land 6a is wider than the port 9, so that there is a short neutral period of the main valve A. While that neutral condition exists, the table cylinder receives no pressure fluid. The length of time during which this neutral condition exists is dependent on the setting of the throttle valve 21. Of course, if it were not for the operation of the pressure fluid to move the spool 7 of the pilot valve B, the main valve would not pass through the neutral position. The present invention, however, assures that the length of this neutral condition or tarry is at a selected value.

A dwell of the table at the left end of its stroke can be achieved by setting the throttle 21 at a selected value. As the pilot spool is pushed to the right by the table, a vacuum is formed in the chamber 16. As the table slows down, the pilot spool already has opened the inlet port 22 and supplied pressure fluid to the line 23. However, the pilot spool proceeds at a very low speed until the pressure, which is needed to move both spools, is built up in the chamber 16. When this occurs, the spools start travelling at a low speed rate until the pilot spool land 70 opens the port 24. After that, the spools will travel with the normal speed to the end. In other words, when the table 1 is being reversed from right-to-left movement to left-to-right movement, the main valve 6 eventually arrives at its dead center position. Because of the connection with the link 5, the spool of the pilot valve is slightly ahead and proceeding to the right. The center land of the pilot valve is slightly to the right of the inlet port 22, so that pressure fluid is allowed to flow through the conduit 23 to the chamber 16 where it presses on the shoulder of the spool and pushes the spool to the right. The movement of the spool is relatively slow, however, because the fluid has to pass through the restriction presented by the throttle 21. This produces a dwell in the movement of the table. Eventually, the spool reaches the point in its movement to the right where the pressure fluid at the port 24 (which fluid does not pass through the throttle 21) can act on the shoulder and produce the final high-speed movement of the spool governed by the throttle 17.

The spool speed control described above makes use of the principle of controlling the flow of oil from the main spool chamber 19, where pressure is being generated, into the chamber 20, where vacuum is being generated. The connections to the exhaust line 25 assure that the leakage of the system is equalized by means of a small oil flow along the ends of the main spool from the exhaust ports 8 and 12 into chambers 19 and 20.

Various other means for controlling the flow of fluid from and to the chambers 19 and 20 are shown in FIGS. 2 through 7. For instance, in FIG. 5, a fixed orifice l7 introduces a preselected restriction into the line 18' joining chambers 19 and 20'. In FIG. 6, it can be seen that the movement of the spool is accomplished by maintaining at a constant value the pressure in the particular chamber where pressure is being developed at any given time. Pressure regulating valves 117 and 117' are located in lines 118 and 118 connected in parallel between the chambers 1 19 and 120.

In FIG. 7, a line 218 joins the chambers 219 and 220. A pressure line 221 is connected to the center of the line and orifices 217 and 217 are located in the line on either side of it. The leakage from the end chambers of the pilot valve is equalized by introducing an equal base pressure into these end chambers; the flow control is superimposed on this base pressure. In a similar manner, in FIG. 8, a pressure line 321 enters a line 318' between check valves 322 and 322', while a fixed orifice 317 lies in a line 318 joining chambers 319 and 320. FIG. 9 shows an arrangement where the pressure line 421 enters a line 418 between two check valves 422 and 422'; the line 418 joins lines 418' and 418" which are connected to end chambers 419 and 420, respectively; at the end of the line 418' is connected through a pressure relief valve 417', while the line 418" is similarly connected to sump through a pressure relief valve 417". In FIG. 10, a pressure line 521 enters a line 418 between two check valves 522 and 522; the line 418 joins lines 418 and 418" connected in parallel between end chambers 519 and S20 and including pressure regulating valves 517 and 517.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent 15:

1. A hydraulic system for reciprocating a machine tool table, comprising a. a table cylinder, I

b. a main control valve having a housing in which a spool reciprocates, there being end chambers formed in the housing into which the ends of the spool extend,

c. a pilot valve having a housing in which a spool reciprocates,

d. a mechanical linkage joining the two spools, the

table controlling the movement of the linkage during certain portions of the cycle of table reciprocation and the spool of the pilot valve operating the movement of the linkage during other portions of the cycle,

e. a throttle valve associated with. the spool of the pilot valve to produce a dwell at the ends of table reciprocation, and

f. a hydraulic connection between the end chambers of the main control valve, including a means for controlling the flow of fluid from one end chamber and the flow of fluid into the other end chamber of the main control valve.

2. A hydraulic system as recited in claim 1, wherein the said means is a flow-regulating throttle inserted in a line directly connecting the end chambers.

3. A hydraulic system as recited in claim 1, wherein the said means includes two pressure relief valves connected in parallel between the two chambers and positioned to open in opposite directions.

4. A hydraulic system as recited in claim 1, wherein a separate fluid pressure supply line is connected to the end chambers to equalize leakage.

5. A hydraulic system as recited in claim 1, wherein a lost-motion connection is provided between the linkage and the spool of the main valve, so that movement of the spool of the main valve always lags movement of the spool of the pilot valve.

6. A hydraulic system as recited in claim 1, wherein an eccentric pin extends from the linkage into a groove in the spool of the pilot valve, the pin being-adjustable to adjust the relative position of the linkage along the spool.

7. A hydraulic system as recited in claim 1, wherein each end of the pilot valve is provided with a land,

whilethe center of the pilot valve has a land which directs pressure fluid to one pressure port or another, wherein each end land is provided with a slow speed port which is connected to the fluid pressure ports through an adjustable throttle valve, wherein a by-pass check valve is connected around each throttle valve, and wherein each fluid pressure port is connected by an unrestricted conduit to a high speed port associated with its respective end land and located inboard of the slow speed port.

8. A hydraulic system for a machine tool, comprising a. a table mounted for reciprocation and having spaced dogs,

b. a lever mounted for pivotal movement about an axis and mounted for engagement by the dogs at the ends of table reciprocation and swingable through a substantial angle by the dogs from a left position to a right position and vice versa,

a hydraulic cylinder for producing table reciprocation, a mam valve having a spool connected by a lostmotion means to the lever at one side of the pivotal axis, the valve being connected to a source of pressure fluid and having a central land for applying the pressure fluid to one end or the other of the cylinder, the spool having two end lands that operate as pistons in end chambers, the end chambers being hydraulically connected through an adjustable restriction, and

. a pilot valve having a spool connected by a position-adjustable means to the side of the lever op posite the connection to the spool of the main valve, the pilot valve being connected to a source of pressure fluid and having a central land for applying the pressure fluid to one of two pressure ports, each end of the spool having a land that operates as a piston in an end chamber, each pressure port being connected through a throttle valve to a slow-speed port entering an end chamber, a by-pass valve being connected around each throttle valve, each pressure port also being connected by an unrestricted conduit to a high-speed port entering the respective end chamber located inboard of the respective slow-speed port. 

1. A hydraulic system for reciprocating a machine tool table, comprising a. a table cylinder, b. a main control valve having a housing in which a spool reciprocates, there being end chambers formed in the housing into which the ends of the spool extend, c. a pilot valve having a housing in which a spool reciprocates, d. a mechanical linkage joining the two spools, the table controlling the movement of the linkage during certain portions of the cycle of table reciprocation and the spool of the pilot valve operating the movement of the linkage during other portions of the cycle, e. a throttle valve associated with the spool of the pilot valve to produce a dwell at the ends of table reciprocation, and f. a hydraulic connection between the end chambers of the main control valve, including a means for controlling the flow of fluid from one end chamber and the flow of fluid into the other end chamber of the main control valve.
 2. A hydraulic system as recited in claim 1, wherein the said means is a flow-regulating throttle inserted in a line directly connecting the end chambers.
 3. A hydraulic system as recited in claim 1, wherein the said means includes two pressure relief valves connected in parallel between the two chambers and positioned to open in opposite directions.
 4. A hydraulic system as recited in claim 1, wherein a separate fluid pressure supply line is connected to the end chambers to equalize leakage.
 5. A hydraulic system as recited in claim 1, wherein a lost-motion connection is provided between the linkage and the spool of the main valve, so that movement of the spool of the main valve always lags movement of the spool of the pilot valve.
 6. A hydraulic system as recited in claim 1, wherein an eccentric pin extends from the linkage into a groove in the spool of the pilot valve, the pin being adjustable to adjust the relative position of the linkage along the spool.
 7. A hydraulic system as recited in claim 1, wherein each end of the pilot valve is provided with a land, while the center of the pilot valve has a land which directs pressure fluid to one pressure port or another, wherein each end land is provided with a slow speed port which is connected to the fluid pressure ports through an adjustable throttle valve, wherein a by-pass check valve is connected around each throttle valve, and wherein each fluid pressure port is connected by an unrestricted conduit to a high speed port associated with its respective end land and located inboard of the slow speed port.
 8. A hydraulic system for a machine tool, comprising a. a table mounted for reciprocation and having spaced dogs, b. a lever mounted for pivotal movement about an axis and mounted for engagement by the dogs at the ends of table reciprocation and swingable through a substantial angle by the dogs from a left position to a right position and vice versa, c. a hydraulic cylinder for producing table reciprocation, d. a main valve having a spool connected by a lost-motion means to the lever at one side of the pivotal axis, the valve being connected to a source of pressure fluid and having a central land for applying the pressure fluid to one end or the other of the cylinder, the spool having two end lands that operate as pistons in end chambers, the end chambers being hydraulically connected through an adjustable restriction, and e. a pilot valve having a spool connected by a position-adjustable means to the side of the lever opposite the connection to the spool of the main valve, the pilot valve being connected to a source of pressure fluid and having a central land for applying the pressure fluid to one of two pressure ports, each end of the spool having a land that operates as a piston in an end chamber, each pressure port being connected through a throttle valve to a slow-speed port entering an end chamber, a by-pass valve being connected around each throttle valve, each pressure port also being connected by an unrestricted conduit to a high-speed port entering the respective end chamber located inboard of the respective slow-speed port. 